1. Field of the Invention:
This invention relates to interchangeable lens barrels which are to be used with motion picture cameras and still cameras, and more particularly to the structure of a composite barrel of the mount for an interchangeable lens which barrel is composed of two distinct sections detachable from each other, one of which is for the mount of a front assembly of a lens system, and the other section which is for the mount of a rear assembly thereof, and which structure permits selection of a plurality of front lens assemblies of different types mounted in the respective front barrel sections for attachment to the rear barrel section provided with a diaphragm drive mechanism incorporated therein.
2. Description of the Prior Art:
Recently in cameras, iris blades used to form an opening to control the incidence of object light, have been positioned within the incidental optical path of the object light, and the size of opening has been made variable by controlling the iris blades so that the photographing can be made with the appropriate exposure. A method for controlling the iris blades is such that an object brightness is detected and the iris blades are controlled by such iris blades driving means as a motor or a galvanometer controlled by signal afforded by the detecting step. Interchangeable lens units housing both the iris blades and the iris blades driving means for operating the iris blades within one interchangeable lens barrel are known. Such a conventional interchangeable lens unit forms one unit having all the optical elements necessary for photographing within itself. But it is necessary for a photographer to prepare many kinds of interchangeable lenses so different arrangements of interchangeable lenses can be used as desired for attaining different photographing effects. However, a conventional interchangeable lens unit housing both the iris blades driving means within one interchangeable lens barrel will have a complicated lens unit structure as the various parts housed within it cause the manufacturing cost to go up, and the price of one interchangeable lens to become high. Therefore, when a photographer wants to photograph with various effects, he needs a number of high priced interchangeable lens units, which results in a considerable economic burden. Providng iris blades and iris blades driving mechanism within each interchangeable lens unit makes the size of the unit that much bigger and heavier, leaving a problem that the unit is inconvenient for handling.